1. Field of the Invention
The present invention relates to a self contained transportable power source maintenance and charge system for an implantable medical device encased in a sterile package. More specifically, the system includes a ribbon cable on a sterile plastic or blister package containing an implantable medical device. The system is connected to the ribbon cable, which in turn is coupled to the medical device, whereby a desired maintenance charge can be maintained on a battery of the medical device until the sterile package is opened for implanting the device.
Rechargeable lithium ion batteries are known for their high voltage and high energy density. Compared to nickel cadmium or nickel metal hydride batteries, lithium ion batteries contain 1.5 times more capacity, 3 times higher voltage with 1.5 to 2 times less weight. Unlike other rechargeable batteries, lithium ion batteries do not exhibit a memory effect, they are friendly to the environment and may be recharged in excess of 500 cycles while retaining acceptable capacity.
Another desirable feature of a lithium ion battery is that properly charged and discharged, lithium ion batteries do not produce gases; hence, they could be enclosed in a hermetically sealed enclosure.
With these attractive technical features in mind, lithium ion batteries may be utilized to power implantable devices.
Nevertheless, certain rechargeable lithium ion electrochemical cells and batteries require a specific voltage and or charge capacity control during storage or transit in order to preserve cell functional integrity. Due to cell chemistry, the cells exhibit a self discharge rate that may over time reduce the voltage down to a detrimental level. If the cell's voltage is allowed to discharge below a specific threshold voltage, prior to charging, the cell's ability to be recharged to the maximum specified capacity may be permanently lost. This loss of recharge capacity is usually referred to as faded capacity. Further, if the cell's voltage is allowed to drop to near zero volts, the cell's ability to be recharged at all may be permanently lost, rendering the cell useless. A known electrochemical mechanism that could cause irreversible damage to a lithium ion cell is dissolution of the current collector material upon voltage reduction below certain threshold.
Therefore, it becomes desirable to have a self contained transportable power source maintenance and charge system that can be pre-programmed to maintain a specific voltage and/or charge capacity of a power source, such as a lithium or any other rechargeable secondary power sources, that is affected by self discharge and its consequential damage.
2. Description of the Prior Art
Heretofore various battery power source charging systems have been proposed. Examples of some of these previously proposed systems are disclosed in the following U.S. patents:
U.S. Pat. No. Patentee 5,411,537 Munshi et al. 5,631,537 Armstrong 5,670,862 Lewyn 5,675,235 Nagai 5,764,030 Gaza 5,811,959 Kejha 5,818,199 Beard 5,880,576 Nagai